Add a DEBUG-only "name" field to vm_area_vector_t, for logging

_From [byron.c....@gmail.com](https://code.google.com/u/101184679827294438523/) on October 08, 2014 23:46:34_

Currently the vmarea logging for add_vm_area and remove_vm_area does not indicate which vectors are being modified, because the vectors have no readable identifier. By adding a DEBUG-only "name" field, the log statements can specify the vector, making it easier to understand what's happening in the vectors, especially when debugging. Additional log statements at level 3 or 4 can specify the reason for vector modification at the call sites of add_vm_area and remove_vm_area (which are all contained within vmareas.c).

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1553_